Method for controlling disengageable clutches for starting and for shifting variable-speed gears in automobiles

ABSTRACT

Control of shiftable clutches by a clutch control signal that is a function of the difference between the actual and desired engine rotational speeds and of the gradient of the actual engine rotational speed and wherein the clutch control signal values are generated by the employment of a set of clutch engagement and disengagement speed curves.

The invention relates to a method for control of shiftable clutches forshifting gears in automobiles.

When connecting a variable-speed gear with the output shaft of aninternal combustion engine, the regulation of the speed at which theclutch is engaged constitutes a problem. If the clutch is engaged tooquickly, there is the danger that the clutch plates and also other partsin the gear and input traction will be damaged.

BACKGROUND OF THE INVENTION

In EP 0 228 544 is disclosed a method for the control of clutch-controlsystems, such as mentioned above, in which a comparator compares theactual rotational speed of the engine with a desired rotational speed.The corresponding output signal, which indicates the difference betweenthe desired rotational speed and the actual rotational speed, is plottedin a summing element and on a differential element which from thedifference produces the temporary change of the difference and plots iton the summing element. The sum resulting from difference and temporarychange of the difference is plotted in a clutch regulator for control ofthe separating clutch.

The problem on which this invention is based consists in providing amethod with which the shiftable clutches are better controlled for thepurpose of starting and shifting variable-speed gears of automobiles.

SUMMARY OF THE INVENTION

With the aid of the instant invention power-shiftable gears having wetclutches can be regulated to a constant slip time, the PI regulatingalgorithms having simple dependences. In this invention, it isadvantageously possible to eliminate the use of PI regulatingalgorithms. This invention can be used specially in relation with theactuation of clutches and motor vehicles for the purpose of starting andchanging gears in stepped transmissions having manual gear shift control(so-called semiautomatic) and in automated gear shifts.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and embodiments are described in detail below with the aidof figures, in which:

FIG. 1 is the block gear shift diagram of a preferred starting and gearshifting device; and

FIG. 2 is a diagram for explaining the calculation of the coupling anduncoupling speed of a clutch according to engine rotational speedgradient and differential rotational speed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, the engine of a motor vehicle 4 is designated with 1. Theseparating clutch that connects the output shaft of the engine 1 withthe gear 2 is designated with 3. The gear 2 acts upon the input gears ofthe motor vehicle 4. The tractional resistance, acting upon the motorvehicle 4, is diagrammatically shown by the arrow 5.

The throttle or accelerator pedal of the vehicle 4 is designated with 6.Via an electronic transmitter (not shown) there is produced on theoutputs of the accelerator pedal 6 an electric signal α which indicatesthe accelerator pedal angle of the throttle pedal. By a computer 7 inwhich the signal α is plotted via a line 61, there is calculated fromthe signal α a signal T_(mot) on a line 8 which leads to the engine 1and by which the signal T_(mot) corresponding to the accelerator angle αis plotted to actuate the fuel injection pump of the engine 1. For thispurpose, the computer unit contains dependences of all possibleaccelerator pedal angles α of the accelerator pedal 6 and correspondingsignals T_(mot) for the injection pump.

Corresponding to the actual rotational speed n_(ist) of the engine 1, asignal is produced on a line 11 by a rotational speed sensor (not shownin detail). The signal is plotted in the summing element 9 in which isalso plotted a signal corresponding to the desired rotational speedn_(soll), which signal generates from a digital unit 10 where the signalα corresponding to the accelerator pedal angle of the vehicle pedal 6 isconverted, based on stored tables and functions, to the set rotationalspeed n_(soll). The signal α is plotted via the line 62 on the digitalunit 10 which is connected via the line 101 with the summing element 9.

The summing element 9 produces on its output 91 a differentialrotational speed signal n_(soll)−n_(ist) which is multiplied by areinforcing factor K2 in a multiplication element 13. The output signalof the multiplication element 13 is plotted via the line 131 on oneother summing element 12 and is there added up with a signal dn/dt whichindicates the gradient of the rotational speed of the engine. The signaldn/dt is produced from the rotational speed signal n_(ist) which abutson the line 11 and is plotted on a differential element 15. The signaldn/dt produced on the output of the differential element 15 ispreferably multiplied by a factor K1 in a multiplication element 14 andthereafter plotted on the summing element 12 via the line 141.

On the output (line 121) of the summing element 12 then abuts a signalwhich comprises both the gradient dn/dt of the engine rotational speedn_(ist) and the difference between the rotational speeds n_(soll) andn_(ist). From said signal α control signal dp/dt for the separatingclutch 3 is produced in a multiplication element 16 by multiplying by afactor fl.

FIG. 2 shows a diagram of the dependence of the difference between setrotational speed n_(soll) and actual rotational speed n_(ist) of theengine 1 from the gradient dn/dt of the engine rotational speed forcalculating the coupling and uncoupling speed of the separating clutch3.

The speed of the engagement and disengagement of the separating clutch 3is here determined in the diagram of FIG. 2 in the form of linear curvesI, II, Ill determined by the difference between set rotational speedn_(soll) and engine rotational speed n_(ist) and the gradient dn/dt,which curves indicate in percent numbers the speed of engagement anddisengagement of the clutch 3. The curves I, II, III are preferablystraight lines that extend parallel to each other and diagonally inrelation to the axis of the gradient, each line corresponding to aspecific speed of the engagement and disengagement of the separatingclutch 3. Therefore, a computer can calculate respectively from a valueof the mentioned difference and a value of the mentioned gradient thespeed for engagement and disengagement.

Different operations are explained in detail below.

When starting, the coupling operation begins when a defined threshold ofthe rotational speed of the accelerator pedal angle a has been exceeded.Each accelerator pedal angle a corresponds to a set rotational speedn_(soll) of the engine 1 and therewith to the primary rotational speedof the separating clutch 3 on which the starting operation develops.

From the formal dependence of the difference n_(soll)−n_(ist) and of thegradient dn/dt of the primary rotational speed on the separating clutch3, there is calculated the speed of the engaging movement which leads toa constant course of the primary rotational speed on the separatingclutch 3. The time until the torque balance is reached on the separatingclutch 3 is here constant, that is, independent of the output state. Asfixed parameter is required only the inertia moment of the driving sideand a conversion factor to convert the torque increase on the separatingclutch 3 to a coupling speed. The above mentioned time can also beprogrammed variable such as dependent on the accelerator pedal angle.Advantageously no expensive regulating algorithm is required. Thecoupling speed is iteratively calculated within a fixed time screen.

When opening the separating clutch 3 for gear change, depending on themomentary magnitude of the torque in the drive train, the filling of theseparating clutch 3 before it opens is reduced. A factor formed from theratio of a reference acceleration of the vehicle to the actualacceleration corrects the filling recirculation depending on the powerexcess. After expiration of the load-reducing phase, the separatingclutch 3 opens in rapid movement. The clear signal for the gear changeis indicated from the moment a defined travel position of the separatingclutch 3 is exceeded.

When closing the separating clutch 3 after a gear change, the closingoperation starts with the information of the terminated gear change.After reaching an engagement degree dependent on the accelerator pedalangle which is started at maximum speed, the regulated couplingoperation begins. Corresponding to the “start” operation, the closingspeed is calculated from the gradient dn/dt of the primary rotationalspeed and the amount of the difference between n_(soll) and n_(ist). Theset value is the secondary rotational speed of the clutch. The enginetorque is increased according to a dependence of the transmitted torqueas function of the clutch path. As added limitation of the clutch load,the engine torque is limited according to the difference between primaryand secondary rotational speeds on the separating clutch 3. Thereby itis not possible, e.g. an “overspeeding” of the clutch due to drop offriction value such as can occur by oiling up etc., for the engine 1 hasbeen backed up.

The regulated closing operation terminates when the synchronousrotational speed has been reached on the separating clutch 3. It is ofthe essence here that the time up to reaching the synchronous speed,which is also designated as slip time, be constant and within certainlimits independently of the friction value fluctuations and frictionlining materials.

After uniformity between the primary and the secondary rotational speedshas been reached, the separating clutch 3 is fully closed at a constantspeed dependent on the acceleration pedal angle. The increase of thebevel of the adjusting device for measuring the fuel up to the valuecorresponding to the position of the accelerator pedal, remains coupledto the clutch path until full closure.

Reference Numerals

1 engine

2 gear

3 separating clutch

4 motor vehicle

5 arrow (tractional resistance)

6 accelerator pedal

7 computer

8 line

9 summing element

10 digital unit

11 line

12 summing element

13 multiplication element

14 multiplication element

15 differential element

16 multiplication element

61 line

62 line

91 output

101 line

121 line

131 line

141 line

What is claimed is:
 1. A method of controlling a shiftable separating clutch (3) for the purpose of starting and shifting variable-speed gears (2) of a motor vehicle (4) comprising the steps of: delivering an actual rotational speed signal (n_(ist)) from an engine (1) to a differential element (15) and a first summing element (9), the actual rotational speed signal (n_(ist)) sent to the differential element being used to calculate a gradient of the engine rotational speed (dn/dt), the engine rotational speed (dn/dt) being sent to a second summing element (12); delivering an electric signal (α) from a throttle (6) to a fuel injection pump and a digital unit (10), the digital unit (10) converts the electric signal (α) to a desired rotational speed signal (n_(soll)), the desired rotational speed signal (n_(soll)) is sent to the first summing element (9); calculating a differential signal (n_(soll)−n_(ist)) by summing in the first summing element (9), the desired rotational speed signal (n_(soll)) and the gradient of the engine rotational speed (dn/dt), the differential signal (n_(soll)−n_(ist)) being sent to a second summing element (12); calculating a clutch control signal (dp/dt) in the second summing element (12) from the differential signal (n_(soll)−n_(ist)) and the gradient of the engine rotational speed (dn/dt); and clutch control signal (dp/dt); and using the clutch control signal (dp/dt) to control the speed of engagement and disengagement of the separating clutch (3).
 2. The method according to claim 1, further comprising the step of multiplying in a first multiplication element (13) said differential signal (n_(soll)−n_(ist)) by a first factor (K2), said first multiplication element (13) being rear-mounted in a second summing element (12).
 3. The method according to claim 1, further comprising the step of multiplying in a second multiplication element (16) rear-mounted on said first summing element (9), the clutch control signal (dp/dt) by a second factor (fl).
 4. The method according to claim 1, further comprising the step of multiplying in a third multiplication element (14) rear-mounted on said differential element (15), the gradient of the engine rotational speed (dn/dt) by a third factor (K1).
 5. A method of controlling a shiftable separating clutch (3) for the purpose of starting and shifting variable-speed gears (2) of a motor vehicle (4) comprising the steps of: delivering an actual rotational speed signal (n_(ist)) from an engine (1) to a differential element (15) and a second summing element (12), the actual rotational speed signal (n_(ist)) sent to the differential element being used to calculate a gradient of the engine rotational speed (dn/dt), the engine rotational speed (dn/dt) being sent to a second summing element (12); delivering an electric signal (α) from a throttle (6) to a fuel injection pump and a digital unit (10), the digital unit (10) converts the electric signal (α) to a desired rotational speed signal (n_(soll)), the desired rotational speed signal (n_(ist)) is sent to the first summing element (9); calculating a differential signal (n_(soll)−n_(ist)) by summing in the first summing element (9), the desired rotational speed signal (n_(soll)) and the gradient of the engine rotational speed (dn/dt), the differential signal (n_(soll)−n_(ist)) being sent to a second summing element (12); and calculating in a computer, a clutch control signal (dp/dt) from the differential signal (n_(soll)−n_(ist)) and the gradient of the engine rotational speed (dn/dt), for controlling the speed of the engagement and disengagement of the separating clutch (3), the clutch control signal (dp/dt) being stored in the computer, depending on a difference between the desired rotational speed signal (n_(soll)) and the actual rotational speed signal (n_(ist)), the same as on the gradient of the engine rotational speed (dn/dt), the computer also storing a curve (I, II, III) as function of the difference between the desired rotational speed signal (n_(soll)) and the actual rotational speed signal (n_(ist)), the same as on the gradient of the engine rotational speed (dn/dt).
 6. The method according to claim 5, further comprising the step of multiplying in a first multiplication element (13) said differential signal (n_(soll)−n_(ist)) by a first factor (K2), said first multiplication element (13) being rear-mounted in a second summing element (12).
 7. The method according to claim 5, further comprising the step of multiplying in a second multiplication element (16) rear-mounted on said first summing element (9), the clutch control signal (dp/dt) by a second fractor (fl).
 8. The method according to claim 5, further comprising the step of multiplying in a third multiplication element (14) rear-mounted on said differential element (15), the gradient of the engine rotational speed (dn/dt) by a third factor (K1). 